1. Field of the Invention
The subject matter disclosed generally relates to the field of hard disk drives.
2. Background Information
Hard disk drives contain a plurality of magnetic heads that are coupled to rotating disks. The heads write and read information by magnetizing and sensing the magnetic fields of the disk surfaces. There have been developed magnetic heads that have a write element for magnetizing the disks and a separate read element for sensing the magnetic fields of the disks. The read element is typically constructed from a magneto-resistive material. The magneto-resistive material has a resistance that varies with the magnetic fields of the disk. Heads with magneto-resistive read elements are commonly referred to as magneto-resistive (MR) heads.
Each head is attached to a flexure arm to create an subassembly commonly referred to as a head gimbal assembly (“HGA”). The HGA's are attached to an actuator arm that has a voice coil coupled to a magnet assembly. The voice coil and magnet assembly create a voice coil motor that can pivot the actuator arm and move the heads across the disks.
Information is typically stored within annular tracks that extend across each surface of a disk. The voice coil motor can move the heads to different track locations to access data stored onto the disk surfaces. Each track is typically divided into a plurality of adjacent sectors. Each sector may have one or more data fields. Each data field has a series of magnetic transitions that are decoded into binary data. The spacing between transitions define the bit density of the disk drive. It is generally desirable to provide a high bit density to increase the overall storage capacity of the drive.
FIG. 1 schematically shows the layer of a disk 1 that is commonly referred to as an anti-ferromagnetic (AFC) media. The AFC media includes a S1 magnetic layer 2 located over a substrate 3. The S1 layer 2 and substrate 3 are typically separated by an underlayer 4 that strengthens the adhesion of the S1 material.
The S1 magnetic layer 2 is covered with a layer of ruthenium 5 and a top layer of magnetic material 6. The top magnetic layer 6 is protected with an overcoat layer 7, typically a diamond-like-carbon (DLC). The overcoat layer 7 may be covered with a layer of lubricant 8 to minimize any frictional contact between the head and the disk.
AFC media with a layer of ruthenium have been found to have a low thermal decay rate at high density recording. Although it has a lower thermal decay rate, AFC media with a layer of ruthenium has a signal to noise ratio (SNR) that limits the bit density of the hard disk drive. To increase the bit density of the disk drive it is desirable to increase the signal to noise ratio of the disk.